This invention generally pertains to a bipolar semiconductor device having a conductive recombination layer. Generally, in semiconductor devices of this type, it is desirable to have a relatively high switching speed while maintaining a reduced "on" state voltage. Commonly, there is a high level of minority carriers in the voltage-blocking semiconductor region which must be removed before a semiconductor device of this type may be turned off. Removing the minority carriers takes a relatively long period of time and results in heating throughout the device. However, if no minority carriers are provided, the "on" state voltage will be extremely high due to a high resistance throughout the semiconductor region of the device. Therefore, a recombination layer which would reduce but not eliminate the minority carrier concentration in the voltage-blocking semiconductor region of a device would be highly desirable.
In the past, methods of doping semiconductor devices with impurities such as gold and nickel resulted in faster minority carrier recombination during the turn off of the device thereby increasing the switching speed. However, since these impurities were present throughout the device, a large voltage drop was caused. Therefore, a recombination layer disposed between layers of varying doping concentration has been found to be highly desirable.